Microsoft Security Bulletin MS13-073 - Important

General Information

Executive Summary

This security update resolves three privately reported vulnerabilities in Microsoft Office. The most severe vulnerabilities could allow remote code execution if a user opens a specially crafted Office file with an affected version of Microsoft Excel or other affected Microsoft Office software. An attacker who successfully exploited the most severe vulnerabilities could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

This security update is rated Important for all supported editions of Microsoft Excel 2003, Microsoft Excel 2007, Microsoft Excel 2010, Microsoft Excel 2013, Microsoft Excel 2013 RT, and Microsoft Office for Mac 2011; it is also rated Important for supported versions of Microsoft Excel Viewer and Microsoft Office Compatibility Pack. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerabilities by correcting how Microsoft Excel and other affected Microsoft software validates data when parsing specially crafted Office files and by correcting the manner in which the XML parser used by Excel resolves external entities within a specially crafted file. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Customers can configure automatic updating to check online for updates from Microsoft Update by using the Microsoft Update service. Customers who have automatic updating enabled and configured to check online for updates from Microsoft Update typically will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates from Microsoft Update and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers apply the update at the earliest opportunity using update management software, or by checking for updates using the Microsoft Update service.

For customers of Microsoft Office for Mac, Microsoft AutoUpdate for Mac can be configured to deliver updates for Microsoft software directly to your system. For more information, see Check for Office for Mac updates automatically.

See also the section, Detection and Deployment Tools and Guidance, later in this bulletin.

Knowledge Base Article

Affected and Non-Affected Software

The following software has been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

[1]For Microsoft Office Excel 2007, in addition to security update package 2760583, customers also need to install the security update for Microsoft Office Compatibility Pack (2760588) to be protected from the vulnerabilities described in this bulletin.

[3]Microsoft Excel Viewer must be updated to a supported service pack level (Excel Viewer 2007 Service Pack 3) before installing this update. For information about supported Office viewers, see Microsoft Knowledge Base Article 979860.

CVE-2013-1315 is described in multiple security bulletins. How are these bulletins related?The Microsoft Office Memory Corruption Vulnerability (CVE-2013-1315) affects the following products:

Microsoft Excel (MS13-073)

Microsoft Office Services and Web Apps (MS13-067)

You need to install only the updates that correspond to the software you have installed on your system. If you need to install more than one of these updates, they can be installed in any sequence.

Why does this update address several reported security vulnerabilities?This update contains support for several vulnerabilities because the modifications that are required to address these issues are located in related files.

What components of the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats are updated by this bulletin?The update included with this security bulletin applies only to the specific component within the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats that is affected. For example, in an Excel bulletin, only the Excel compatibility pack component files are included in the update packages and not Word or PowerPoint compatibility pack component files. Word compatibility pack component files are updated in a Word bulletin and PowerPoint compatibility pack component files are updated in a PowerPoint bulletin.

How are Microsoft Office standalone programs affected by the vulnerabilities?A Microsoft Office standalone program is affected with the same severity rating as the corresponding component in a Microsoft Office Suite. For example, a standalone installation of Microsoft Excel is affected with the same severity rating as an installation of Microsoft Excel that was delivered with a Microsoft Office Suite.

The Microsoft Office component discussed in this bulletin is part of the Microsoft Office Suite that I have installed on my system; however, I did not choose to install this specific component. Will I be offered this update?Yes, if the component discussed in this bulletin was delivered with the version of the Microsoft Office Suite installed on your system, the system will be offered updates for it whether the component is installed or not. The detection logic used to scan for affected systems is designed to check for updates for all components that were delivered with the particular Microsoft Office Suite and to offer the updates to a system. Users who choose not to apply an update for a component that is not installed, but is delivered with their version of the Microsoft Office Suite, will not increase the security risk of that system. On the other hand, users who do choose to install the update will not have a negative impact on the security or performance of a system. For more information on this behavior and recommended actions, see Microsoft Knowledge Base Article 830335.

Does the offer to update a non-vulnerable version of Microsoft Office constitute an issue in the Microsoft update mechanism?No. The update mechanism is functioning correctly in that it detects a product version for the applicable software on the system that is within the range of product versions that the update applies to and thus, offers the update.

I am using an older release of the software discussed in this security bulletin. What should I do?The affected software listed in this bulletin has been tested to determine which releases are affected. Other releases are past their support life cycle. For more information about the product lifecycle, see the Microsoft Support Lifecycle website.

Customers who require custom support for older software must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, see the Microsoft Worldwide Information website, select the country in the Contact Information list, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Microsoft Support Lifecycle Policy FAQ.

Vulnerability Information

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the September bulletin summary. For more information, see Microsoft Exploitability Index.

A remote code execution vulnerability exists in the way that Microsoft Excel parses content in Excel files. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2013-1315.

Mitigating Factors

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

In a web-based attack scenario, an attacker could host a website that contains a specially crafted Office file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker’s website, and convince them to open the specially crafted Office file.

An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

The vulnerability cannot be exploited automatically through email. For an attack to be successful a user must open an attachment that is sent in an email message.

Workarounds

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

You can block specific types of files from being opened or saved in Excel, PowerPoint, and Word by configuring settings in either Group Policy or the Office Customization Tool (OCT). For more information about preventing users from opening specific types of files in Microsoft Office, see Plan File block settings.

To use file block to help protect from exploitation of the vulnerabilities, configure file block to block *xls, *.xla, *.xlt, *.xlm, *.xlw, and *.xlb binary documents and templates for all affected versions of Microsoft Excel.

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources. This vulnerability could be exploited when a user opens a specially crafted file.

FAQ

What is the scope of the vulnerability?This is a remote code execution vulnerability.

What causes the vulnerability?The vulnerability is caused when affected versions of Microsoft Excel and other affected Microsoft Office software does not properly handle objects in memory while parsing specially crafted Office files.

What might an attacker use the vulnerability to do?An attacker who successfully exploited this vulnerability could cause arbitrary code to run in the security context of the current user. If the current user is logged on with administrative user rights, an attacker could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability?This vulnerability requires that a user open a specially crafted Office file with an affected version of Microsoft Excel or other affected Microsoft Office software.

In an email attack scenario, an attacker could exploit the vulnerability by sending a specially crafted Office file to the user and by convincing the user to open the file.

In a web-based attack scenario, an attacker would have to host a website that contains a specially crafted Office file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit this vulnerability. An attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link that takes them to the attacker's site, and then convince them to open the specially crafted Office file.

What systems are primarily at risk from the vulnerability?Systems where Microsoft Excel is used, including workstations and terminal servers, are primarily at risk. Servers could be at more risk if administrators allow users to log on to servers and to run programs. However, best practices strongly discourage allowing this.

What does the update do?The update addresses the vulnerability by correcting how Microsoft Excel and other affected Microsoft software validates data when parsing specially crafted Office files.

When this security bulletin was issued, had this vulnerability been publicly disclosed?No. Microsoft received information about this vulnerability through coordinated vulnerability disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers when this security bulletin was originally issued.

A remote code execution vulnerability exists in the way that Microsoft Excel parses content in Excel files. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2013-3158.

Mitigating Factors

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

In a web-based attack scenario, an attacker could host a website that contains a specially crafted Office file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker’s website, and convince them to open the specially crafted Office file.

An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

The vulnerability cannot be exploited automatically through email. For an attack to be successful a user must open an attachment that is sent in an email message.

Workarounds

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

You can block specific types of files from being opened or saved in Excel, PowerPoint, and Word by configuring settings in either Group Policy or the Office Customization Tool (OCT). For more information about preventing users from opening specific types of files in Microsoft Office, see Plan File block settings.

To use file block to help protect from exploitation of the vulnerabilities, configure file block to block *xls, *.xla, *.xlt, *.xlm, *.xlw, and *.xlb binary documents and templates for all affected versions of Microsoft Excel.

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources. This vulnerability could be exploited when a user opens a specially crafted file.

FAQ

What is the scope of the vulnerability?This is a remote code execution vulnerability.

What causes the vulnerability?The vulnerability is caused when affected versions of Microsoft Excel and other affected Microsoft Office software does not properly handle objects in memory while parsing specially crafted Office files.

What might an attacker use the vulnerability to do?An attacker who successfully exploited this vulnerability could cause arbitrary code to run in the security context of the current user. If the current user is logged on with administrative user rights, an attacker could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability?This vulnerability requires that a user open a specially crafted Office file with an affected version of Microsoft Excel or other affected Microsoft Office software.

In an email attack scenario, an attacker could exploit the vulnerability by sending a specially crafted Office file to the user and by convincing the user to open the file.

In a web-based attack scenario, an attacker would have to host a website that contains a specially crafted Office file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit this vulnerability. An attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link that takes them to the attacker's site, and then convince them to open the specially crafted Office file.

What systems are primarily at risk from the vulnerability?Systems where Microsoft Excel is used, including workstations and terminal servers, are primarily at risk. Servers could be at more risk if administrators allow users to log on to servers and to run programs. However, best practices strongly discourage allowing this.

What does the update do?The update addresses the vulnerability by correcting how Microsoft Excel and other affected Microsoft software validates data when parsing specially crafted Office files.

When this security bulletin was issued, had this vulnerability been publicly disclosed?No. Microsoft received information about this vulnerability through coordinated vulnerability disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers when this security bulletin was originally issued.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2013-3159.

Mitigating Factors

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

The vulnerability cannot be exploited automatically through email. For an attack to be successful a user must open an attachment that is sent in an email message.

In a web-based attack scenario, an attacker could host a website that contains a specially crafted Office file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker’s website, and convince them to open the specially crafted Office file.

Workarounds

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources

Do not open Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources. This vulnerability could be exploited when a user opens a specially crafted file.

FAQ

What is the scope of the vulnerability?This is an information disclosure vulnerability. An attacker who successfully exploited this vulnerability could read data from a file located on the target system. Note that this vulnerability would not allow an attacker to execute code or to elevate their user rights directly, but it could be used to produce information that could be used to try to further compromise the affected system.

What causes the vulnerability?The vulnerability is caused when Microsoft Excel improperly handles XML external entities that are resolved within other XML external entity declarations.

What is an XML External Entity?An XML document may consist of one or many storage units. These are called entities. They all have content and are all identified by entity name. External entities allow an XML document to refer to an external file. External entities contain either text or binary data. If they contain text, the content of the external file is inserted at the point of reference and parsed as part of the referring document.

What might an attacker use the vulnerability to do?An attacker who successfully exploited this vulnerability would be able to read data from files on the target system. Note that this vulnerability would not allow an attacker to execute code or to elevate their user rights directly, but it could be used to produce information that could be used to try to further compromise the affected system.

How could an attacker exploit the vulnerability?Exploitation of this vulnerability requires that a user open a specially crafted file with an affected version of Microsoft Office.

In an email attack scenario, an attacker could exploit the vulnerability by sending a specially crafted file to the user and by convincing the user to open the file in an affected version of Microsoft Excel.

In a web-based attack scenario, an attacker would have to host a website that contains an file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit this vulnerability. An attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince them to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes them to the attacker's site, and then convince them to open the specially crafted file in an affected version of Microsoft Excel.

What systems are primarily at risk from the vulnerability?This vulnerability requires that a user open a specially crafted file with an affected application for any malicious action to occur. Therefore, any systems where Excel files are frequently viewed, such as workstations or terminal servers, are at the most risk from this vulnerability.

What does the update do?The update addresses the vulnerability by correcting the manner in which the XML parser used by Excel resolves external entities within a specially crafted file.

When this security bulletin was issued, had this vulnerability been publicly disclosed?No. Microsoft received information about this vulnerability through coordinated vulnerability disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers when this security bulletin was originally issued.

In some cases, this update does not require a restart. If the required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.

To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update. For more information about the reasons why you may be prompted to restart, see Microsoft Knowledge Base Article 887012.

Removal information

Use Add or Remove Programs item in Control Panel.

Note When you remove this update, you may be prompted to insert the Microsoft Office 2003 CD in the CD drive. Additionally, you may not have the option to uninstall the update from the Add or Remove Programs item in Control Panel. There are several possible causes for this issue. For more information about the removal, see Microsoft Knowledge Base Article 903771.

In some cases, this update does not require a restart. If the required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.

To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update. For more information about the reasons why you may be prompted to restart, see Microsoft Knowledge Base Article 887012.

In some cases, this update does not require a restart. If the required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.

To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update. For more information about the reasons why you may be prompted to restart, see Microsoft Knowledge Base Article 887012.

In some cases, this update does not require a restart. If the required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.

To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update. For more information about the reasons why you may be prompted to restart, see Microsoft Knowledge Base Article 887012.

Microsoft Excel 2013 RT (all editions)

In some cases, this update does not require a restart. If the required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.

To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update. For more information about the reasons why you may be prompted to restart, see Microsoft Knowledge Base Article 887012.

Removal information

Click Control Panel, click System and Security, click Windows Update, and then under See also, click Installed updates and select from the list of updates.

Office for Mac 2011

Download and install the appropriate language version of the Microsoft Office for Mac 2011 14.3.7 Update from the Microsoft Download Center.

Quit any applications that are running, including virus-protection applications and all Microsoft Office applications, because they might interfere with installation.

Open the Microsoft Office for Mac 2011 14.3.7 Update volume on your desktop. This step might have been performed for you.

To start the update process, in the Microsoft Office for Mac 2011 14.3.7 Update volume window, double-click the Microsoft Office for Mac 2011 14.3.7 Update application, and follow the instructions on the screen.

When the installation finishes successfully, you can remove the update installer from your hard disk. To verify that the installation finished successfully, see the following "Verifying Update Installation" heading. To remove the update installer, first drag the Microsoft Office for Mac 2011 14.3.7 Update volume to the Trash, and then drag the file that you downloaded to the Trash.

Verifying Update Installation

To verify that a security update is installed on an affected system, follow these steps:

In the Finder, navigate to the Application Folder (Microsoft Office 2011).

Select Word, Excel, PowerPoint or Outlook and launch the application.

On the Application menu, click About Application_Name (where Application_Name is Word, Excel, PowerPoint or Outlook).

If the Latest Installed Update Version number is 14.3.7, the update has been successfully installed.

Restart Requirement

This update does not require you to restart your computer.

Removing the Update

This security update cannot be uninstalled.

Additional Information

If you have technical questions or problems downloading or using this update, see Microsoft for Mac Support to learn about the support options that are available to you.

Other Information

Acknowledgments

Microsoft thanks the following for working with us to help protect customers:

Will Dormann of the CERT/CC for reporting the Microsoft Office Memory Corruption Vulnerability (CVE-2013-1315)

Will Dormann of the CERT/CC for reporting the Microsoft Office Memory Corruption Vulnerability (CVE-2013-3158)

Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please go to the active protections websites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

V1.0 (September 10, 2013): Bulletin published.

V1.1 (September 13, 2013): Revised bulletin to announce detection changes for the Microsoft Excel 2003 update (2810048), Microsoft Excel 2007 update (2760583), Microsoft Excel Viewer update (2760590), and Microsoft Office Compatibility Pack update (2760588). These are detection changes only. There were no changes to the update files. Customers who have successfully installed the updates do not need to take any action. Also updated the Known Issues entry in the Knowledge Base Article section from "Yes" to "None".